1. Field of the Invention
The present invention relates to a thermosetting resin composition for an underfilling of a semiconductor, and to a semiconductor device produced using it.
2. Related Background Art
With ongoing trends toward smaller and higher performance electronic devices in recent years, semiconductor devices that are smaller, thinner and have improved electrical characteristics (such as applicability for high-frequency transmission) are in demand. A simultaneous shift has begun from systems in which semiconductor chips are mounted on boards by conventional wire bonding, to flip-chip connection systems in which conductive protruding electrodes known as a “bumps” are formed on semiconductor chips for direct connection with board electrodes.
The bumps formed on semiconductor chips include bumps composed of solder or gold, but recent years have seen increasing use of bumps that have structures with solder layers or tin layers formed on the tips of copper bumps or copper pillars, for suitability to formation of microconnections.
Connections using metal joints are also desired in order to achieve higher reliability, and such methods are being employed not only with solder joints using solder bumps, or metal joints formed by bumps having structures with solder layers or tin layers formed on the tips of copper pillars, but also when using copper bumps or gold bumps, by forming solder layers or tin layers on the board electrode side and creating metal joints.
In flip-chip connection systems as well, since thermal stress created by the difference in thermal expansion coefficients of the semiconductor chips and board can potentially be concentrated at the joints and damage the joints, it is necessary to underfill the gap between the semiconductor chips and board with a resin, in order to disperse the thermal stress and increase the connection reliability. Generally speaking, underfilling with a resin is accomplished using a system in which the semiconductor chips and board are connected with solder or the like, and then the liquid sealing resin is injected into the gap by capillary flow.
For connection between chips and a board, it is common to use flux composed of a rosin or organic acid, to allow removal of the oxide layer on the solder surface by reductive reaction to facilitate metal melting. If flux residue remains in such cases, it can cause generation of air bubbles known as voids when the liquid resin is injected, or corrosion of wiring can occur due to the acid component, thus lowering the connection reliability, and therefore a step of residue cleaning has been required. However, it is often difficult to accomplish cleaning of flux residue because of the narrower gap between the semiconductor chips and board when the connection pitch becomes smaller. In addition, productivity may be reduced because it takes a longer time to inject the liquid sealing resin into the narrower gap between the semiconductor chips and board.
In order to overcome these problems with the liquid sealing resin, there have been proposed connecting methods known as “pre-applied systems” in which a sealing resin having a property allowing removal of the solder surface oxide layer (flux activity) by reductive reaction is applied to the board, and then the gap between the semiconductor chips and board are underfilled with the resin as the semiconductor chips and board are connected, thus allowing cleaning of the flux residue to be skipped, and underfilling resins suitable for such connection systems have been developed (see Patent documents 1-3, for example).
With the goal of shortening the connection process, there is increased interest in wafer processes wherein an underfilling resin layer is formed on the bump-formed side of the semiconductor wafer, which is then individuated into semiconductor chips, thereby creating a plurality of resin layer-formed chips, and the semiconductor chips are connected with a board, and underfilling resins suited for such processes are also being actively developed (see Patent documents 4-6, for example).